1. Field of the Invention
The present invention is directed to a disinfection system for the inactivation of microorganisms such as bacteria, viruses, fungi, parasites, etc., in water. More particularly, the present invention is directed to a disinfection system of a permanganate, and copper and silver ions. This system provides a high level of reduction in the number of microorganisms in a reduced period of time, as well as a high rate of inactivation. The present invention is further directed to a method of disinfecting water using the system of the present invention.
2. Background of the Prior Art
Because of its importance and ubiquity of application, methods for the disinfection of water have received long-term and widespread attention. Disinfection, as used in this specification, refers to the destruction or irreversible inactivation of infectious or other undesirable microorganisms such as bacteria, pathogenic fungi, parasites, viruses and the like. Various techniques for water disinfection have been developed to render affected water potable or simply less odiferous.
Generally, the more practical techniques involve the addition of a disinfecting agent to the water. Agents commonly used in this regard include halogens, oxidants other than halogen, and metals, either in free or salt form.
Of the halogens, chlorine is the most widely used. Chlorine may be added to water in any number of ways, such as direct addition of elementary chlorine or by addition of chlorine-containing compounds, including calcium hypochlorite, sodium hypochlorite, chlorine dioxide or chloramines. It is believed that the disinfecting action of chlorine gas, the hypochlorites and the chloramines is due primarily to the release of hypochlorous acid [HOCl) as well as the likely contributory effect of the hypochlorite ion (OCl.sup.-) As to chlorine dioxide, it is believed that the disinfecting action is attributable to chlorite (ClO.sup.-.sub.2) and/or chlorate (ClO.sup.-.sub.3) ions.
Despite its popularity, chlorination suffers from several drawbacks. For example, chlorine gas, the hypochlorites and the chloramines lose much of their potency under practical conditions of disinfection, such as when organic matter is present, owing to the intense reactivity of both the hypochlorous acid and the hypochlorite ion. Further, the chloramines are generally much less effective than hypochlorous acid: they require more time and higher concentrations to achieve effective disinfection. The use of chlorine dioxide also has disadvantages which are primarily health related in that it is believed the residual by-products, i.e., the chlorite and chlorate ions, have adverse physiological effects. Indeed, chlorination has been found to contribute to the formation of numerous chlorinated organic compounds in water. These compounds, e.g., trihalomethanes, are known or suspected to be hazardous to human health
Other oxidants, separate and apart from the halogens, have also been investigated to determine their efficacy as regards water disinfection. Most prominent among these are ozone and the permanganates, especially potassium permanganate. Ozone is an active disinfectant in the presence of water and has been used mainly in connection with the disinfection of water in swimming pools. However, ozone has a very high oxidation potential which results in the ability of the water to carry any residual that is present. Further, ozone is more expensive to employ than other, more readily available disinfectants, such as chlorine-based agents.
Potassium permanganate in water has been used for the removal and control of iron and manganese in surface water supplies, as well as for the removal of odors caused by organic matter and microbial growth. In addition, because of its broad microbial properties, potassium permanganate has been used for the disinfection of drinking water. This particular use, however, has fallen out of favor since potassium permanganate produces a residue, i.e., manganese dioxide, as an oxidation by-product, which residue is toxic and generally requires removal during conventional water treatment practices of flocculation, sedimentation and filtration.
To mitigate the deleterious effects attendent the use of chlorine-based compounds or potassium permanganate at the concentrations required for the separate use of these materials, systems combining these two disinfectants have been investigated. For example, Yahya, et al. in the Journal of Environmental Science and Health, Vol. 24, No. 8 (1989) envisage the use of potassium permanganate as an adjunct to chlorination, allowing the amount of chlorine to be reduced while still maintaining the requisite inactivation of viruses.
Other methods of disinfecting water include the use of metals, either in free form or salt form. Metals most often used for this purpose include copper and silver which have a long history in this regard, the preservation of water by storage in silver or copper vessels being known to the Persians. Current methods usually require the generation of copper and/or silver ions, generally by electrolytic means. For example, U.S. Pat. No. 4,680,114 to Hayes relates a water purification apparatus especially useful for swimming pools. The apparatus is comprised of electrodes formed with copper and silver; electric current causes copper and silver ions to pass into solution, thus destroying bacteria, algae and other microorganisms.
Thurman and Gerba, CRC Critical Reviews in Environmental Control, Vol. 18, No. 5, Pages 295-315 (1989) examine the possible mechanisms responsible for the disinfecting properties that copper and silver have on bacteria and viruses.
While halogens, oxidants other than halogens and metals have been used individually for disinfection purposes, various combinations of these have also been investigated. Examples of these attempts include U.S. Pat. No. 4,492,618 to Eder, which relates a method for disinfecting swimming pool water using copper and silver ions in conjunction with sodium persulfate. The sodium persulfate is described as releasing oxygen when under the influence of copper and silver ions, thus causing the oxidation of organic substances.
Studies have also been performed using combinations of copper and silver ions with free chlorine to reduce bacterial numbers in water environments. For example, the Journal of Environmental Health, Vol. 51, No. 5, Pages 282-285 (1989) reports the use of copper and silver ions in combination with 0.2 milligrams per liter (mg/L) of free chlorine; the Water Pollution Control Federation Specialtv Conference Series, Page 85 et seq. May 29-June 2, 1989 relates the use of copper and silver ions in combination with 0.1-0.4 mg/L of free chlorine, and Water Science and Technoloqv, Vol. 21, No. 3, Pages 267-270 (1989) describes anti-microbial activity for a combination of copper and silver ions with and without low levels (0.2-0.3 mg/L) of free chlorine.
However, given the health concerns involved in the use of chlorine and chlorine-based disinfectants, these methods are less than desirable for most practical applications.
Thus the water disinfection art recognizes a continuing need to find disinfection systems and methods that are effective, economical, have high levels and rates of inactivation, and are easy to implement and do not pose the threat to human health or the environment that currently attend known practices.